1. Field of the Invention
The present invention relates to a magnetic recording element and a magnetic memory utilizing a magnetization reversal by the spin-polarized electrons.
2. Description of the Related Art
In recent years, the research and development of spintronics devices by using the freedom degree of electron spins have been performed actively.
For instance, in a hard disk drive, a magnetization state of a recording medium is controlled by a magnetic field from a magnetic head, while in a magnetic random access memory, a magnetic state of a magnetoresistive element is controlled by a composite magnetic field from two write lines.
Such a method of controlling the magnetization state using the magnetic field has a long history, and it has already become an established technique.
On the other hand, because of the recent progress in nanotechnology, the miniaturization of the recording unit of the recording medium and the magnetoresistive element has advanced, and thus there is a need to perform control of the magnetization state locally on a nano scale.
However, it is difficult for the magnetic field to be localized since the magnetic field has characteristics to diverge spatially. For this reason, erroneous writing occurs by the effect of the magnetic field on the recording unit and the magnetoresistive element other than the object of the writing, that is, crosstalk occurs. Further, when attempting to achieve localization of the magnetic field by minimizing the generation source of the magnetic field, the magnetic field with enough magnitude for the magnetization reversal cannot be obtained.
Accordingly, “current induced magnetic switching” in which such a problem does not occur, has been attracting attention (For instance, refer to F. J. Albert, et al., Appl. Phy. Lett. 77, 3809 [2000]).
This is a technique in which a current as a write current is caused to flow in the magnetoresistive element, and then the magnetization reversal is executed while using spin-polarized electrons generated therein. Specifically, the magnetization of a magnetic free layer is inverted by the fact that angular momentum of the spin-polarized electrons is transferred to the angular momentum of a magnetic material serving as the magnetic free layer.
By using such a magnetization reversal technique due to the current (current induced magnetization reversal), the magnetization state is easily controlled locally with nano-meter scale, and it is possible to reduce the switching current with miniaturization of the magnetic element. Therefore, it helps realization of spin-electronic devices such as the magnetic recording with high recording density or the magnetic random access memory.
However, there is a challenge in this technique as well. That is, a current density Jc for the magnetization reversal is typically 1×107 A/cm2 or more. Such a large value induces the problem of reliability such that element characteristic degradation.
As countermeasures against this problem, for instance, some proposals have been made such as reducing the value of the saturated magnetization Ms of the magnetic material constituting the magnetoresistive element (for instance, refer to JP-A 2005-93488 [KOKAI], JP-A 2004-193595 [KOKAI]). However, when reducing the saturated magnetization Ms in conventional magnetic recording elements, new problems occur in which thermal fluctuation resistance and magnitude of the reproducing signal output deteriorate.